I’m almost certain that earlier versions of iOS exposed the comma on the main keyboard and hid the period under the symbols button, because double-tapping space added it.

Which meant that, depending on version, you’d sometimes need to tap 6 times to write “…” (to enter the symbols keyboard mode after every period, since it would go back to the primary set every time), and only 3 to write “,,,”.

But I might be wrong.